1 Samuel 27:10-12

10Then Achish would say, “Where have you made a raid today?” And David would say, “Against the southern area of Judah, or against the southern area of the Jerahmeelites, or against the southern area of the Kenites.”

11David would save neither man nor woman alive, to bring news to Gath, saying, “Lest they should inform on us, saying, ‘Thus David did.’ ” And thus was his behavior all the time he dwelt in the country of the Philistines.

12So Achish believed David, saying, “He has made his people Israel utterly abhor him; therefore he will be my servant forever.”